I heard from several people that they preferred to buy their own modem and router in order to get the maximize speed they're supposed to get. Do you guys do it? Is it preferred to buy your own stuff rather than using the company's router/modem?

Most routers allow for much greater transfer speeds than the internet line is limited to. The only advantage of using faster routers is for local network data transfer, like when you have a NAS.
As for the modem, as long as it gives you the full internet speed you are supposed to have hen there's no need to change it.

Tadashi pretty much summed it up there. However, there are a few things about routers that you want to know:

1. There are two different "bands", 2.4 ghz and 5 ghz
A. The 2.4 ghz band tends to be more "crowded", thus possibly effecting connectivity. This is because, when multiple routers run off the same "channel", the signals overlap, causing disruptions in your wifi. This is normally fixed by changing said channel in your router settings. However....
B. If that doesn't work, you want to switch to the less used 5ghz band. The problem? It's not common for a reason. Download a network analyzer on your Android Device (or PC) and check the difference between the two. It's like day and night. Not all routers use 5ghz. However, some use both 2.4 and 5. Another thing to note us that 5ghz doesn't work as well through surfaces.

2.4 ghz is where people get the "wifi is shit compared to ethernet" idea from. However, 5ghz speeds are nearly identical to ethernet speeds (in my case, anyway.)

Note, however, that not all devices support 5ghz, in which case you want an ethernet cord if possible(the Playstations are such an example).

Anyway, to answer the topic, I use an ISP-supplied modem and a hone-bought dual-band router.

WiFi AC routers(the ones with 5GHz support) are too expensive(at the time of writing) for most people's practical applications, I wouldn't recommend them. Especially with how most devices can't use WiFi AC. Only top of the line laptops/phones have WiFi AC support.

Top-of-the-line? I can only partially agree with that. I own an Insignia Flex 10.1, priced at $120. It most certainly has 5ghz support (and trust me, it helps). The only device I know of without 5ghz would be the Playstation 4. Low-end laptops can be supplemented with a USB dongle that supports 5ghz, like this; http://www.walmart.com/ip/Linksys-Dual-B...r/22027096

As for it being expensive, the Linksys EA4500 has a very respectable $100 pricepoint, and it's dual-band, allowing for both a 2.4 and 5ghz connection.

All-in-all, it may seem expensive, but it's easy to find a fair price on something good. After all, the EA4500 is SO much better than any other router I've used, and it's been around for quite a while (4 or so years, now?)